On 09.03.2014 23:53, David Miller wrote: > To me it means "I've got nothing to do if other tasks want to run right > now" Yes, I even see it having this meaning when an RT task executes > it. http://www.kernel.org/doc/htmldocs/device-drivers/API-yield.html lists this exact "while (!event) yield;" pattern as a broken usage and states "Never use yield as a progress guarantee!!". > How else can you interpret the intent above? IMNSHO there is no way to make the yield() honor this intent if it is called from a SCHED_FIFO or SCHED_RR task and the task unblocking it is running at a lower priority. On the PREEMPT_RT systems where the interrupt handlers are threads an application thread running at higher priority than some interrupt handlers is a common situation. The semantics of the scheduler here is "run the highest priority runnable task until it blocks (FIFO) or its time slice is over and there are more with the _same_ priority (RR)". This scenario then collapses into a busy loop never making progress. > If you change it to msleep(1), you're assigning an extra completely > arbitrary time limit to the yield. The code doesn't want to sleep > for 1ms, that's not what it's asking for. The problem is that there is no way to formulate what it is asking for in scheduler terms only. Regards -- Stano -- To unsubscribe from this list: send the line "unsubscribe linux-rt-users" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
